Aircraft: MEDIUM LARGE TRANSPORT; LOW WING; 2 TURBOJET ENG
Phase of flight: Landing
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach

After changing Runways from 16R to 16L; we executed the LOC 16L approach. First Officer (FO) was the flying pilot. At MDA; FO left MDA early to accommodate the landing; only to trigger a response from SEA tower that there was a 'low altitude alert'. I advised tower that we had the airport in sight. Due to lack of maintaining 'LOC Only' MDA experience that appeared to be manifesting itself at that moment; I elected to assume aircraft control from FO but stating 'My Airplane'. The FO transferred control to me; and I executed an uneventful landing in the touch down zone of Runway 16L. This was the third and final leg of a scheduled 11-hr duty day. ATIS reported VFR conditions (10sm; BKN038); no report of rain in the vicinity; although TAF did forecast -RA. ATIS reported windshear. I reviewed windshear procedures. I also used a personal app and requested landing runway data to compute/assess crosswind. This was only my second arrival to SEA in 30 days; so I also spent time plotting various taxiway closures due to construction. We were cleared to descend via HAWKZ landing south to expect 16R. I had briefed a visual approach backed up by ILS for 16R. Controller later said we would be vectored east of field for left downwind to 16R for sequencing. We were handed off to final controller on heading 040 at 220 knots. We confirmed intentions for 16R with final controller. Just prior to base turn controller said 16L was released for non-heavy aircraft. We agreed to accept 16L; Captain (CA) reprogrammed the FMC for 16L ILS; while I pulled up the chart and dialed in the localizer freq. we quickly reviewed frequencies and final approach course and set a course for the FAF in the FMC. I still expected a visual approach; and did not brief minimums. We were given a dog leg and cleared to intercept the localizer for 16L at 4000 feet. I had slowed to 180 and dropped the gear while tracking the localizer outside of a 10 mile final. Controller asked us to maintain 200 knots; and asked if we could accept RNAV. We replied negative due to time/range to the airport. The Controller said he would have to step us down for the localizer. This was first time that we became aware of Glide Slope Out of Service (it was NOTAM'd out; and we missed it in the ATIS between taxiway closures and windshear advisories). I could now see rain showers but assumed that it would be good visibility underneath a layer that appeared to be around 1500 feet. Controller cleared us down to 3200; but did not specify speed restriction. We passed inside of KARFO at 3200 feet and 200 knots; and I began to verbalize my concern over the energy state. The Captain started to coach me; saying I could start slowing. We were then cleared the Localizer approach for 16L at about 7-8 DME and 3200 feet. The Captain then briefed the MDA to me; and I set my Baro bug; and rapidly reduced power to continue configuring. I had to level off to slow enough for flaps 25-30. There was now steady rain; and I asked for wipers. I started a steep descent to recapture the path. The CA reported that I was now on path; and stated he could see approach lights. I then got behind my cross check; and did not arrest my descent to capture the MDA on speed. CA stated he had VASI in sight; I did not. He was now more positively coaching me on power and attitude to recapture MDA. The Controller gave us a 700 feet call and the Captain replied field in sight. I then saw the VASI and approach end; I was not stable however. CA took the aircraft for an uneventful landing. The crew accepted a late runway change; unaware that the glideslope was out of service. They received a low altitude alert from the Tower although the Captain had the field in sight. The Captain took the aircraft from the First Officer and landed uneventfully.